This invention relates to a control circuit for controlling such electric coupling apparatus as an electromagnetic clutch and an electromagnetic brake.
Electromagnetic coupling apparatus effecting buffer coupling are disclosed in Japanese Utility Model Publication Nos. 22293/1972 and 15647/1973 by the same applicant as the present application. The electromagnetic coupling apparatus disclosed in these utility model publications comprise a plurality of armatures and the number of attracted armatures is gradually increased according to the excitation of an exciting coil. However, where the load driven by the electromagnetic coupling apparatus varies greatly, as an armature is initially attracted, a friction noise is generated or a sufficient coupling force is not obtained with the result that coupling is delayed, thus failing to provide desired buffer coupling.
In the past, a simple switch has been used for controlling the electromagnetic coupling apparatus such that the current flowing through the exciting coil can be ON-OFF controlled. Such a control device can not eliminate the problem described above and the advent of an improved control circuit has been desired which is structurally improved and suitable for buffer coupling.